Local proximity just makes it easier to hold for any Solly force who tries to invade

You simply have to realize that there are only a number of different possible strategies a commander can use :
1) Invasion with the goal of holding the new territories. It's simply stupid to leave enemy pickets in your rear area if you are conducting an invasion becaus these pickets provide rally points for resistance and unsually offer reapairs and reammunitions for enemy forces conducting operations in your conquered territory. That's standard military doctrine and I don't see a reason why this should be invalidated in the Honorverse.
2) Diversionary Attacks: Attacks in the deep rear area. Like the Peeps did with Alizon and Zanzibar. Intended to spread the available forces thin an reduce the possiblity of an counter offensive. There is no reason to suspect the Sollies would use this.
3) Commerce Raiding: Like 2) there is no reason to suspect the Sollies would use this.
4) Decisive Offensive: Like the Battle of Manticore. Something unheared of so far. Note that the BoM ist still in the future or at least the news have not reached Monica yet.
5) Striking important military assets: There are not yet any realy important *military* targets in the Quadrant which would be a primary target.

I had the same idea.
What's so special about these ships? Why can only Mesa build them? And the only answer I came up was because they are bio-engineered warships. Like ... fully automated Shrike LACs ... they could theoretically achieve much higher accelleration rates because there is no crew onboard ...
that could prove to be a problem even for apollo SD(P)s

I don't think the SEM has the right to confiscate every ship that enters it's star systems
there has to be a valid charge or it would be unlawfull ... no one would be that stupid but they could just fabricate charges ...
and now think: The "Antilope" never even existed. So what's the problem about saying it was unlawfully seized by Manty authorities?
And in my opinion, and as far as I have understood interstellar law, an unlawfull seizeing of ships equals piracy

I think they are gonna try to provoke an incident ... this is just the buildup
first they complain about harrassment and produce some evidence, second they are gonna play propaganda like "evil Manties" and when the Tuscan public is angry enough somebody ist gonna say "We have to do something about this. The Manties are even worse than the OFS" ... and this leads to third: They are gonna call the Sollies for "protection of the open trade" from the Manticorans or they are gonna acuse the Manty officers of outright piracy and this will lead to an OFS investigation ...

although the RMN should enforce customs inspections it's not unusual for the local authorities to do so if no RMN vessel is available or the vessel is unwilling ... I just think of Basilisk where the civilians did them ...